Intraocular lenses (IOLs) are implanted in patients' eyes either to replace a patient's lens or, in the case of a phakic IOL, to complement the patient's lens. For example, the IOL may be implanted in place of the patient's lens during cataract surgery. Alternatively, a phakic IOL may be implanted in a patient's eye to augment the optical power of the patient's own lens.
Some conventional IOLs are single focal length IOLs. Single focal length IOLs have a single focal length or single power. The focal length is generally fixed at a point relatively close to the patient, for example on the order of one meter from the patient. Objects at the focal length from the eye/IOL are in focus, while objects nearer or further away are out of focus. Although objects are in perfect focus only at the focal length, objects within the depth of field (within a particular distance of the focal length) still acceptably in focus for the patient to consider the objects in focus. However, patients may still require additional correction for objects that are closer or further away than the depth of field.
Some conventional IOLs may utilize diffraction to provide multiple focal lengths. Such conventional diffractive IOLs typically have two focal lengths-far and near. Diffractive IOLs utilize a diffraction grating formed on the anterior surface of the IOL. The diffractive grating typically takes the form of microscopic echelettes, or surface saw-tooth like facets, formed on the lens surface. The echelettes form a diffraction grating having a particular focal length. For example, some conventional bi-focal diffractive IOLs may break the lens into zone plates based upon distance from the optic axis. Each zone includes a single echelette having a radius of curvature proportional to the square root of the zone number, with odd zones having a step height for the echelette and even zones having half of the step height for the echelette. Such a conventional diffractive IOL may have two focal lengths. However, such a diffractive IOL may still have a limited depth of field around each focal length. As a result, a patient may still require additional correction for activities, such as reading, that may involve focusing objects outside of the depth of field for each focal length.
Accordingly, what is needed is a system and method for improving the depth of field in IOLs.